package Final;

import java.util.Map;
import java.util.Scanner;
public class test17{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Point p1 = new Point(sc.nextDouble(),sc.nextDouble());
        Point p2 = new Point(sc.nextDouble(),sc.nextDouble());
        Line l = new Line(p1,p2);
        System.out.printf("%.2f",l.getLength());
    }
}

/* 请在这里填写答案 */
class Point{
    double x;
    double y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }
}
class Line{
    Point p1;
    Point p2;

    public Line(Point p1, Point p2) {
        this.p1 = p1;
        this.p2 = p2;
    }
    public double getLength(){
        return Math.sqrt(Math.pow(p1.x - p2.x,2) + Math.pow(p1.y - p2.y,2));
    }
}